Package for nonaqueous electrolyte cell and cell comprising the same

ABSTRACT

There is provided a package for a non-aqueous electrolytic battery by which water invasion from outside is lowered and adhesion strength is improved over the long term, and a non-aqueous electrolytic battery having a lengthened life and high reliability. 
     In a package for a non-aqueous electrolytic battery having a bag construction to store a battery content made by adhesion of a part of a lamination film comprising a metal layer and a resin layer, the adhesion part holds a structure capable of reacting with or absorbing an element which diffuses from the battery interior inwardly to the battery interior side.

TECHNICAL FIELD

The present invention relates to a package for non-aqueous electrolyticbattery. More particularly, the present invention relates to a packagefor non-aqueous electrolytic battery which can prevent water frominvading externally and strength from decreasing over the long term andlengthen life and heighten reliability of the battery, and relates to anon-aqueous electrolytic battery whose life is lengthened andreliability is heightened by using said package.

BACKGROUND ART

Downsizing and weight saving of batteries are needed for smaller andlighter portable electronic devices. Lithium ion batteries are regardedas the most suitable secondary battery for achieving the object becauseof the high voltage and high energy density, and are being activelyupgraded. One of the important points for the upgrade of the battery isto replace recent metal outer housing of the battery with a lighterpackage comprising a film such as an aluminum laminated film or thelike. Such a package comprising a film is prepared by thermal meltingand adhesion of a part of a folded film covering a battery content, andis formed like a bag.

Compared to the currently used metal outer housings, these packagescomprising films have inferior blocking against water invading into abattery and insufficient strength because of its adhesion part, whichpossibly causes troubles with long-term battery performance orreliability in high temperature.

The present invention has been carried out in order to solve the aboveproblems. The object of the present invention is to provide a batterypackage for a non-aqueous electrolytic battery such as lithium ionbatteries, using a laminated film, by which water blocking is ensuredand strength is maintained easily for a long time, and to provide abattery using the same.

As a means for improving the reliability of these packages, there are,for example, a process for maintaining credible sealing by laminating aprotective film at a heat-sealed part as shown in Japanese UnexaminedPatent Publication No. 40114/1999 and a process for maintaining crediblesealing by constructing a heat-sealed part with a plurality of resins,i.e., a material having superior barrier performance against electrolyteand a material having excellent vapor barrier performance as shown inJapanese Unexamined Patent Publication No. 274896/1997. However, theseprocesses have problems with increase of package weight and complicatedsteps.

DISCLOSURE OF INVENTION

The present inventors have found some important facts about waterblocking and durability of adhesion strength concerning a package for anon-aqueous electrolytic battery using a laminated film. It was foundthat a trace of reactive substance diffused into the adhesion layer fromthe package interior side, leading to decrease of water blocking andadhesion strength of the package. The reactive substance in a tracequantity seems to comprise substance separated from electrolytic saltsuch as acid including hydrogen fluoride, or PF₅. Diffusion of thesubstance causes deterioration of the adhesion layer or an aluminumlayer, resulting in decrease of water blocking performance and adhesionstrength. The laminated film can hold a structure capable of reactingwith or absorbing a diffusing element to inhibit the diffusion from thebattery interior. However this process causes unfavorable phenomena suchas decrease in adhesion strength and increase in water diffusion fromoutside. Prevention of the diffusion from the battery interior withoutaffecting performance of the adhesion part is highly effective inimproving package performances.

More specifically, the present invention relates to: a package fornon-aqueous electrolytic battery, having a bag construction to store abattery content made by adhesion of a part of a lamination filmcomprising a metal layer and a resin layer, wherein the adhesion partholds a structure capable of reacting with or absorbing an element whichdiffuses from battery interior inwardly to the battery interior side;the package for a non-aqueous electrolytic battery, wherein adhesion ofthe film is performed by using a hot-melt adhesive in the form of tapecontaining a structure capable of reacting with or absorbing A anelement which diffuses from battery interior; the package for anon-aqueous electrolytic battery, wherein adhesion of the film isperformed by a hot-melt adhesive in the form of tape containing, inparallel to the longitudinal direction, a filament structure capable ofreacting with or absorbing an element which diffuses from batteryinterior; a battery using the package for a non-aqueous electrolyticbattery.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view schematically showing the adhesion partof the package for a non-aqueous electrolytic battery according to oneembodiment of the present invention.

FIG. 2 is a cross-sectional view schematically showing the constructionof the non-aqueous electrolytic battery prepared in Example 1.

In FIG. 1, numeral 1 indicates an aluminum layer, 2 a polypropylenelayer, 3 an adhesive layer, 4 adhesion part and 5 a structure capable ofreacting with and absorbing an element which diffuses from the batteryinterior.

In FIG. 2, numeral 4 indicates the adhesion part, 5 an aluminum fiber, 6a rolled out electrode, 7 a terminal for current collection (a tab) and8 a package for non-aqueous electrolytic battery.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention relates to a package for non-aqueous electrolyticbattery, having a bag construction storing a battery content made byadhesion of a part of a lamination film comprising a metal layer and aresin layer, wherein the adhesion part holds a structure capable ofreacting with or absorbing an element which diffuses from the batteryinterior.

The film used for the package is formed by laminating at least a metallayer and a resin layer which coats the package interior side of themetal layer.

Metal foil such as aluminum foil, stainless foil or titanium foil can beused for the metal layer. The thickness of the metal layer is preferably3 to 200 μm, more preferably 10 to 100 μm. Too thin a metal film tendsto cause easy generation of defects such as pinholes, leading toinferior reliability. Too thick a metal layer tends to cause increase ofweight. The surface of the metal foil may be treated so that an oxidefilm or a nitride film is formed thereon in order to improve endurance.

As to the resin layer, any resin layer may be available as long as itdoes not dissolve into an electrolytic solution and prevents the metallayer from corroding. A polyolefin film such as polypropylene,polyethylene or a copolymer thereof is preferably used as the resinlayer. Other useful films include a film comprising a fluorine resin, avinyl polymer such as polystyrene, a cross-linked acrylic resin and thelike. The thickness of the resin layer is preferably 5 to 200 μm, morepreferably 20 to 100 μm. When the resin layer is thin, steadyheat-sealing tends to become difficult. When the resin layer is thick,the strength at the heat-sealing part tends to decrease.

An adhesive can be used for the adhesion of the metal layer and theresin layer, if necessary. Coating or film lamination onto the packageexterior side of the metal layer is also preferable for improvingstrength and preventing corrosion.

The package of the present invention has a bag construction made byadhesion of a part of a lamination film comprising a metal layer and aresin layer. An adhesive can be used for the adhesion of the film. Ahot-melt adhesive is preferable as the adhesive for the adhesion of thefilm in terms of workability, moisture permeability or the like. Whenpolyolefin is used for the resin layer of the film, this can be used asthe hot-melt adhesive for the adhesion of the film. An epoxy adhesive ora urethane adhesive can be also used as long as it is resistant toelectrolytes. These adhesives can be used in combination of two or more.The resin layer at the adhesion part of the film may be removed ifrequired. In this case attention should be paid not to expose the metallayer to the package interior, and not to generate defects such as crackon the metal layer. Also useful is a hot-melt adhesive in the form oftape.

The elements which diffuses from the battery interior are substanceseparated from electrolytic salt such as acid including hydrogenfluoride, or PF₅ depending on kinds of battery (electrode orelectrolyte).

Useful as the structure capable of reacting with or absorbing theelement which diffuses from the battery interior are metal such asaluminum or iron, an inorganic material such as carboxylate or metaloxide, salt of polymer containing carboxylic acid such as methacrylicacid, acrylic acid or maleic acid, polymers containing a basic groupsuch as an amino group, and the like. Preferably, these substances mayalso be surface-treated to fit with the material constituting theadhesion layer if necessary.

The useful shape for the structure capable of reacting with or absorbingthe element which diffuses from the battery interior is powdery, flakyor filament form while a material of a variety of sizes can be usedconsidering the width and the length of the adhesion part and the like.

As to the structure made of powder, for example, particle size thereofis preferably about 0.1 to 100 μm, more preferably about 1 to 20 μm.When the particle size is small there is a tendency that the particlescannot be added to the adhesive effectively. When it is large there is atendency that diffusion cannot be prevented sufficiently.

As to the structure made of flakes, for example, thickness thereof ispreferably about 0.5 to 200 μm, more preferably 5 to 100 μm. When it isthin there is a tendency that diffusion cannot be prevented effectively.When it is thick heat-sealing tends to be difficult. Referring to thearea, the longest diameter is preferably about five times, morepreferably about ten times the thickness. In this flaky structure it iseasier for each structure part to be aligned, and diffusion of thenon-aqueous solvent is prevented effectively. When the longest diameteris too short the alignment of the structure tends to be difficultleading to decrease of the advantage.

As to the structure made of filaments, for example, filament diameterthereof is preferably about 0.1 to 200 μm, more preferably about 5 to100 μm while filament length thereof is preferably at least 10 μm, morepreferably at least 5 mm. When the filament diameter is small the effecton preventing diffusion tends to be low. When it is large heat-sealingtends to be difficult. When the filament is short the effect onpreventing diffusion tends to be low.

Filament form is most preferable for merely preventing the element fromdiffusing since it functions most effectively even in a little amount.Particles and porous materials are preferable in terms of the effect onprevention of diffusion by reaction or absorption.

Preferably, the structure capable of reacting with or absorbing adiffusing element is distributed inwardly to the package interior side,that is, at least more to the inside from the centric position betweenthe package exterior side edge and the package interior side edge of theadhesion part. When the structure capable of reacting with or absorbinga diffusing element is not distributed inwardly to the package interiorside, the effect on inhibition of the diffusion of the element whichdiffuses from the battery interior side may be reduced at the adhesionpart, and prevention of water invasion and maintenance of strength maynot be achieved sufficiently.

FIG. 1 schematically shows the adhesion construction of the package fora non-aqueous electrolyte battery 8 with a structure (aluminum fiber) 5capable of reacting with or absorbing the element which diffuses fromthe battery interior side inwardly to the battery interior side at theadhesion part 4, regarding the package for a non-aqueous electrolytebattery 8 having a bag construction to store a battery content made byadhesion of a part of a lamination film of the aluminum layer 1 and thepolypropylene layer 2 with an adhesive 3.

When a hot-melt adhesive in the form of tape is used for adhesion of thefilm, workability is improved by previous inclusion of the structurecapable of reacting with or absorbing the element which diffuses fromthe battery interior into the hot-melt adhesive tape. In this case,diffusion of the element which diffuses from the battery interior can beeffectively inhibited by containing, in the longitudinal direction, thefilament structure capable of reacting with or absorbing the element.

A battery construction using the package of the present invention may bea laminated construction of plane electrodes and a separator, a rolledout construction, a folded construction or a combination thereof.

Current collector terminals (tabs) for the electrode of a battery aredrawn out from the adhesion part of the package. As to adhesion of thispart, a conductive material should not be used for the structure capableof reacting with or absorbing the element which diffuses from thebattery interior in order to maintain insulation. Alternatively, thereshould be another insulating layer near the tabs without the structurecapable of reacting with or absorbing the element which diffuses fromthe battery interior.

As the non-aqueous solvent for an electrolytic solution an ethersolution such as dimethoxy ethane or diethyl ether, or a carbonate orester solution such as ethylene carbonate or propylene carbonate is usedalone or in combination thereof. LiPF₆, LiClO₄, LiBF₄ and the like canbe used as the electrolyte.

Hereinafter more concrete examples of the present invention areexplained in detail but the present invention is not limited thereto.

EXAMPLE 1 Process for Preparing Film

A piece of 15-μm-thick aluminum foil was laminated with a 12-μm-thickfilm of polyethylene terephtharate by using a urethane adhesive(5-μm-thick). A hot-melt resin layer of 50-μm-thick polyethylene waslaminated on the opposite side of the aluminum foil by using a urethaneadhesive (5-μm-thick). The film was cut into a piece of 70 mm×125 mm.

Process for Preparing Battery

In FIG. 2, the construction of a non-aqueous electrolytic batteryprepared in Example 1 is schematically shown. Explanation is made as toa process for preparing a battery with reference to FIG. 2 in thefollowing.

A positive electrode material was prepared by applying a paste for apositive electrode active material obtained by mixing 87% by weight ofLiCoO₂, 8% by weight of a graphite powder (KS-6, available from LONZACo., Ltd.) and 5% by weight of poly(vinylidene fluoride) as a binderresin onto a piece of 20-μm-thick aluminum foil according to DoctorBlade method in a thickness of about 100 μm.

A negative electrode material was prepared by applying a paste for anegative electrode active material obtained by mixing 95% by weight ofmesophase microbeads carbon (available from Osaka Gas Co., Ltd.) and 5%by weight of poly(vinylidene fluoride) as a binder onto a piece of12-μm-thick copper foil according to Doctor Blade method in a thicknessof about 100 μm.

Each of the positive and negative electrode materials was cut into asize of 50 mm×200 mm and current collector terminals (tabs) wereattached thereto. The separator cut into a size of 52 mm×210 mm wasinterposed between the positive electrode and the negative electrode.Upon rolling out the same in a width of about 5 cm, it was fixed byusing a strip of polyimide tape.

Thereafter, the rolled out electrode 6 was interposed by the aluminumlaminated film as shown in FIG. 2, and each side end where no tab ispositioned was heat-sealed in a width of about 7 mm. In this event thealuminum fiber 5 was interposed in the adhesion layer by distributing analuminum fiber 5 having a diameter of about 150 μm at a position about 2mm from the battery interior in the adhesion part 4. The end of thealuminum fiber 5 at the side where the tabs 7 of the battery are drawnout was about 5 mm inward from the edge of the aluminum laminated film.

Then an electrolytic solution of LiBF₆ as an electrolyte in ethylenecarbonate and 1,2-dimethoxyethane as a solvent was injected from aremaining edge followed by preliminary charge. Then the edge washeat-sealed by interposing a 25-μm-wide polyethylene hot-melt adhesivebetween the tabs 7 of the electrode and the aluminum laminated film.

Evaluation of Package Performance

The prepared battery was kept under conditions of temperature of 80° C.and humidity of 100% for four weeks.

After that the battery appearance of the battery was observed whilestrength at the adhesion part was measured based on peeling strengthbefore and after the keeping.

There was no change in the battery appearance after the keeping. As tothe peeled adhesion part, the peeling strength was lowered inside thealuminum fiber, but no significant change of the peeling strength wasfound at the other part as it showed 30 g/cm before the keeping and 25g/cm after the keeping.

EXAMPLE 2

To an ethylene-vinyl acetate copolymer were added 50% by weight ofcalcium carbonate. The mixture was kneaded, melted, formed into film andwas cut to prepare a structure about 300 μm thick and about 0.8 mm wide.

A battery was prepared in the same manner as in Example 1 except thatthe calcium carbonate structure was used instead of the aluminum fiber.In this case the calcium carbonate structure was inserted even into theside of the adhesion part from which the tabs are drawn out as well asinto the both end parts. The structure was inserted between apolyethylene hot-melt adhesion film and an aluminum laminated film.

Evaluation of Package Performance

The prepared battery was kept under the same conditions as in Example 1to evaluate performance of the package.

There was no change in the battery appearance after the keeping. As tothe peeled adhesion part, the peeling strength was lowered inside thecalcium carbonate structure, but no significant change of the peelingstrength was found at the other part as it showed 30 g/cm before thekeeping and 23 g/cm after the keeping.

COMPARATIVE EXAMPLE 1

A battery was prepared in the same manner as in Example 1 but withoutinterposing any aluminum fiber.

Evaluation of Package Performance

The prepared battery was kept under the same conditions as in Example 1to evaluate performance of the package.

The aluminum layer was peeled off from the hot-melt layer at some partsaround the battery after the keeping.

There was significant influence of the substance diffusion from thebattery interior compared to Examples 1 and 2.

EXAMPLE 3

A polypropylene hot-melt adhesive having a thickness of about 30 μm wascut into 7 mm wide. Aluminum fibers having a diameter of 50 μm werefixed thereto by light hot press at a position about 3 mm from an edge.

An aluminum laminated film and battery contents were prepared in thesame manner as in Example 1 and each side end where no tab is positionedwere heat-sealed by using the tapes of the hot-melt adhesive containingthe aluminum fiber. Herein the aluminum fiber was distributed inwardlyto the interior side of the battery. The end of the aluminum fiber atthe tab side of the battery was about 5 mm inward from the edge of thealuminum laminated film. Then electrolytic solution of LiBF₆ as anelectrolyte in ethylene carbonate and 1,2-dimethoxyethane as a solventwas injected from the remaining edge followed by preliminary charge, andthen the edge was heat-sealed in a width of 10 mm by using a25-μm-thickness polyethylene hot-melt adhesive interposed between theelectrode tab part and the aluminum laminated film.

Evaluation of Package Performance

The prepared battery was kept under the same conditions as in Example 1to evaluate performance of the package.

There was no change in the battery appearance after the keeping. As tothe peeled adhesion part, the peeling strength was lowered inside thealuminum fiber, but no significant change of the peeling strength wasfound at the other part as it showed 35 g/cm before the keeping and 30g/cm after the keeping.

EXAMPLE 4

A battery was prepared in the same manner as in Example 1 except forusing the calcium carbonate structure prepared in the same manner as inExample 2 instead of the aluminum fiber. The calcium carbonate structurewas inserted even into the portion of the adhesion part from which thetabs are drawn out as well as to the both side ends. It was interposedbetween the polyethylene hot-melt adhesive film and the aluminumlaminated film.

Evaluation of Package Performance

The prepared battery was kept under the same conditions as in Example 1to evaluate performance of the package.

There was no change in the battery appearance after the keeping. Whenthe adhesion part was peeled off the peeling strength was lowered insidethe calcium carbonate structure, but no significant change was found inthe peeling strength at the other part as it showed 34 g/cm before thekeeping and 27 g/cm after the keeping.

COMPARATIVE EXAMPLE 2

A battery was prepared in the same manner as in Example 3 but withoutinterposing any aluminum fiber.

Evaluation of Package Performance

The prepared battery was kept under the same conditions as in Example 1to evaluate performance of the package.

The aluminum layer was peeled off from the hot-melt layer at some partsaround the battery after the keeping.

It was found that corrosion and decrease of peeling strength could beprevented by using aluminum fibers and the like when Examples 3 and 4were compared with Comparative Example 2.

According to the invention of claim 1, it is possible to provide apackage for a non-aqueous electrolytic battery by which water invasionfrom outside is lowered, and corrosion and decrease in adhesion strengthare small at the adhesion part over the long term.

According to the invention of claim 2, it is possible to provide apackage for a non-aqueous electrolytic battery by which water invasionfrom outside is lowered, and corrosion and decrease in adhesion strengthare small at the adhesion part over the long term with high workability.

According to the invention of claim 3, it is possible to provide apackage for a non-aqueous electrolytic battery by which water invasionfrom outside is especially lowered, and corrosion and decrease inadhesion strength are especially small at the adhesion part over thelong term with high workability.

According to the invention of claims 4 to 6 it is expected to obtain abattery having a lengthened life and high reliability since waterinvasion from outside is lowered, and corrosion and decrease in adhesionstrength are small at the adhesion part over the long term.

INDUSTRIAL APPLICABILITY

The package for a non-aqueous electrolytic battery according to thepresent invention can be applied to not only a lithium ion secondarybattery of an organic electrolytic solution type or a gel electrolytetype, but also for a primary battery such as a lithium battery oranother secondary battery.

What is claimed is:
 1. A package for a non-aqueous electrolytic battery,having a bag construction to store a battery content made by adhesion ofa part of a lamination film comprising a metal layer and a resin layer,wherein the adhesion part holds a structure capable of reacting with orabsorbing an element which diffuses from the battery interior outwardlyto the battery exterior side.
 2. The package for a non-aqueouselectrolytic battery of claim 1, wherein adhesion of the film isperformed by using a hot-melt adhesive in the form of tape containing astructure capable of reacting with or absorbing an element whichdiffuses from battery interior.
 3. The package for a non-aqueouselectrolytic battery of claim 2, wherein adhesion of the film isperformed by using a hot-melt adhesive in the form of tape containing,in parallel to the longitudinal direction, a filament structure capableof reacting with or absorbing an element which diffuses from batteryinterior.
 4. A battery using the package for a non-aqueous electrolyticbattery of claim
 1. 5. A battery using the package for a non-aqueouselectrolytic battery of claim
 2. 6. A battery using the package for anon-aqueous electrolytic battery of claim 3.